Figure 1: Simplified schematics of a CMOS nanowire transistor. A single spin can be trapped below the gate inside a thin silicon on insulator (SOI) channel.

microelectronics industry has shrinked the size of transistors present in our computers and other electronic equipment, arriving to critical sizes on the order of ten nanometers. On the other hand academic researchers have developed a new paradigm for computing based on quantum physics for which the information unit is not a bit "0" or "1" but a quantum bit |j>= a|0> + b|1> named qubit. Qubits can be implemented on different physical media such as photons, Josephson junctions (superconducting junctions), nuclei or electrons. For the latter the spin state (intrinsic magnetic moment) can be used, we then speak about spin qubit.

A collaboration between researchers from CEA-INAC and CEA-LETI, mixed research units CEA-Université Grenoble Alpe, has just highlight that very small silicon transistors manufactured by silicon-on-insulator technology (SOI) are perfect candidates for the production of spin qubit. Indeed we have shown that transistors when cooled close to absolute zero behave as electron traps, allowing the study of the spin state of a single electron, see Figure 1.

More subtly we have not studied an electron but a hole, a particle with its charge and momentum opposite to those of an electron, for which we demonstrate that the spin state responds to the application of an electric field while this response is absent in the case of electron. This unique property of holes in silicon allows imagining future "all electrical" spin qubits in conventional transistors.

Eventually the work presents multiple interests: first for fundamental physics it demonstrates that transistors can be used to explore the quantum properties of spins in silicon, but also for applications as it highlights the potential of conventional transistors for a future quantum computer.